Such a device is known from the article “Determination of Lung Perfusion by Means of Electrical Impedance Tomography,” Henning Luepschen et al., Biomed Tech 2010; 55 (Suppl. 1). The device has an electrical impedance tomography unit (EIT unit), as it is frequently used in medical engineering applications. Such an EIT unit has a plurality of electrodes, which can be placed on the thorax distributed around the circumference of a section plane. Furthermore, a control and analysis unit is present, which is connected with the electrodes and is set up to consecutively feed alternating current or alternating voltage to each pair of the plurality of electrodes and to record the resulting voltage or current signals of the other electrodes as measured signals and to reconstruct the impedance distribution in the section plane from the measured signals. More precisely, what is determined in this case is not the impedance in its absolute value but its change compared to a reference distribution. Such an EIT unit is described, for example, in EP 2 228 009 A1.
Further, a manually operated administering device (e.g., a syringe) is present in the prior-art device for the intravenous administration of a conductivity contrast medium. Liquids whose conductivity differs markedly from that of blood may be used as conductivity contrast media. After administering a bolus of the conductivity contrast medium, regional conductivity dilution curves can be recorded, i.e., the flow of the bolus through the section plane is manifested in a rapid rise in the impedance to a maximum, which is followed by a slower drop to the baseline (if the conductivity contrast medium lowers the impedance, a drop in impedance to a minimum and then a rise to the baseline are seen). Such dilution curves can be recorded for the individual image elements of the reconstructed impedance distribution of the section plane through the thorax and displayed on a display device. The instantaneous determined impedance values can be represented in a spatially resolved manner, for example, in a two-dimensional representation, the instantaneous values being represented by corresponding brightness values. After administering a bolus of the conductivity contrast medium, the inflow of the contrast medium into the right side of the heart, where a correspondingly increased brightness is seen as a result in the image of the section plane of the thorax in the area of the right heart, is then seen at first, for example, after which the contrast medium leaves the right side of the heart in the direction of the lungs, as a result of which the right parts of the heart, which are at first visualized with increased brightness, will again become darker and the lungs become brighter, after which the control medium will then flow back into the left side of the heart, which will then appear with a correspondingly increased brightness on the display device. Instead of a representation of the instantaneous impedance values, which varies over time, it is also possible to display other parameters of the dilution curves in a spatially resolved manner, for example, the maximum amplitude of the dilution curves or the integral value over the dilution curve; an individual, spatially resolved representation of a parameter for lung perfusion would then be generated in the latter cases for the administration of a bolus of the conductivity contrast medium. The term “parameter for lung perfusion” is used here to make it clear that the lung perfusion values do not have to be determined here in terms of their absolute values, but the relative percentages relative to the overall perfusion may be sufficient.
When measuring the lung perfusion with the use of a conductivity contrast medium, the contrast medium must first be injected in order to subsequently start the perfusion measurement on the EIT unit. Two problems arise from this when a measurement is carried out: a) Relative to the administration of the contrast medium, and b) relative to the lung perfusion measurement.
When administering the conductivity contrast medium, the rate at which the contrast medium is administered may sometimes greatly affect the accuracy of the measurement and the comparability of different measurements with one another. This is especially true if the contrast medium is administered manually without determining the exact volume and/or the exact point in time. Insofar as the administration of the contrast medium is performed manually and without technical monitoring, the in vivo concentration of the contrast medium cannot be assumed to be comparable for all measurements, and the quantifiability and comparability of EIT analyses is not consequently guaranteed.
A time shift also arises during the lung perfusion measurement between the administration of the conductivity contrast medium and the start of the measurement. This time shift may already lead to impaired quality of the analytical results. Since, moreover, the time shift cannot be assumed to be always constant, two measurements are comparable with one another only conditionally, because different concentrations of the contrast medium in the blood can be assumed to occur at the respective measurement times. This also applies to the end of the administration of the contrast medium, since the lung perfusion measurement also must be terminated now after a defined time. A time shift between the end of the administration of the contrast medium and the termination of the EIT measurement can be assumed here as well.
Since the measurements may possibly deviate greatly from one another in case of manual administration of the conductivity contrast medium and the results of the measurements are not reproducible, no reliable conclusions can be drawn from the measured values. For example, it is not possible to determine the ventilation-perfusion ratio (V/Q ratio) such that different measurements would be comparable with one another and a trend could thus be detected.